1,4-Dienes are useful as comonomers in polyolefin polymers since they allow the polymer to be crosslinked.
In U.S. Pat. No. 3,405,194 (the '194 patent), Iwamoto et al disclose a method of producing hexadienes by the reaction of an alpha-monoolefin with a conjugated diolefin in the presence of a catalyst system of a salt of cobalt or iron, a tertiary diphosphine, and an organoaluminum compound. Tertiary diphosphines are described in the '194 patent to include 1,2-bis(diphenylphosphino)ethane (herein sometimes abbreviated "dppe") and 1,3-bis(diphenylphosphino)propane (herein sometimes abbreviated "dppp").
In the '194 patent examples and in a number of contemporaneous and subsequent learned scientific publications and patents, the prior art has taught the importance of reacting a conjugated diolefin with an alpha-monoolefin at temperatures of about 80.degree. C. or more when using a cobalt based catalyst system of the types described in the '194 patent.
Of the 88 examples in the '194 patent, 68 examples (1-53 and 74-88) are directed to a catalyst system of a salt of cobalt, a tertiary diphosphine, and an organoaluminum compound, and 64 of these 68 examples employ a temperature of at least 80.degree. C. (example 2 is at 70.degree. C. and examples 39, 47 and 76 are at 50.degree. C., all with a catalyst system including a cobalt complex with dppe).
In "A New Process for 1,4-Diene Synthesis", A. Miyake, G. Hata, M. Iwamoto, and S. Yuguchi, Proceedings of the Seventh World Petroleum Congress, 1967, volume 5, 317, the authors described the superiority of a cobalt diphosphine system of CoCl.sub.2 -dppe in combination with an aluminum trialkyl, specifically, triethylaluminum, at 80.degree. C., in producing 1,4-hexadiene at a rate 100 fold higher than an iron based system of Fe(III)(acetylacetonate).sub.3 -Et.sub.3 Al at 30.degree. C. and 10 fold greater than a FeCl.sub.3 -dppe-Et.sub.3 Al system at 80.degree. C. (each also described in the '194 patent).
The effects of reaction temperature on reaction rate for butadiene conversion are particularly described for the catalyst system of CoCl.sub.2 -dppe-Et.sub.3 Al in "Reaction of Butadiene with Ethylene. IV. Synthesis of 1,4-Hexadiene by a Cobalt Chloride-Ditertiary Phosphine Complex and an Organoaluminum Compound Catalyst", M. Iwamoto and S. Yuguchi, Bulletin of the Chemical Society of Japan, 1968, 41, 150. Apparent optimum reaction temperatures are said to be in the range of 80.degree. to 100.degree. C. Two examples achieved 97% selectivity at 80.degree. C. Below 80.degree. C., rate of conversion is shown to fall precipitously, and at temperatures higher than 100.degree. C. a considerable loss of selectivity from isomerization of 1,4-hexadiene to conjugated dienes, mainly to 2,4-hexadiene, is reported.
Henrici-Olive et al, in "Codimerization of Butadiene and Ethylene," Journal of Organometallic Chemistry, vol. 35, p. 381 (1972), a study of the catalytic system described in the above cited articles by Iwamoto et al, report that temperature of reaction appears "critical" for high selectivity using CoCl.sub.2 -dppe-Et.sub.3 Al in dichloroethane. The authors state that: "between 80.degree. and 110.degree. cis-1,4-hexadiene is formed in high yield, whereas below 80.degree. more ethylene than butadiene is consumed, with the result that C.sub.8 compounds are produced. Above 110.degree. 1,4-hexadiene is isomerized to 2,4-hexadiene." (p. 381). Teaching the same is U.S. Pat. No. 3,647,902, to Henrici-Olive et al (where the catalyst system is CoCl.sub.2 -dppe-Et.sub.3 Al in a halogenated hydrocarbon solvent), stating the temperature must be not less than 80.degree. C. when ethylene is reacted with 1,3-butadiene, or poor selectivity results (col. 2, lines 13-24).
The foregoing teachings in the prior art on conducting the reaction at temperatures of at least 80.degree. C. encompass specific described cobalt catalyst systems where the diphosphine ligand is dppp. In the '194 Patent, examples 18-27, 43 and 88 employ dppp as a cobalt catalyst ligand. In examples 18-27, the cobalt complex is CoCl.sub.2 and dppp; in examples 43 and 48, the cobalt complex is the acetyl acetonate of trivalent cobalt, i.e., Co(C.sub.5 H.sub.7 O.sub.2).sub.3, with the dppp ligand. (Herein, for brevity and clarity, acetylacetonate is sometimes referred to by the abbreviation "acac"; for example, the acetylacetonate of trivalent cobalt is Co(acac).sub.3). The dppp ligand thus is Co(acac).sub.3 -dppp. The organoaluminum compound used in examples 18-27, 43 and 88 is trimethylaluminum ("TMAL") or triethylaluminum ("TEAL") when the cobalt salt is CoCl.sub.2 and is sometimes diethylaluminum chloride ("DEAC") when the cobalt salt is Co(acac).sub.3. In all these '194 patent examples employing the dppp ligand, the temperatures are in the range 80.degree.-102.degree. C.
"Effects of Ditertiary Phosphine Ligands in Co-dimerization of Butadiene and Ethylene Catalyzed by Cobalt Chloride-Ditertiary Phosphine-Triethylaluminum" T. Kagawa, Y. Inoue, and H. Hashimoto, Bulletin of the Chemical Society of Japan, 1970, 43, 1250, reports results for testing a CoCl.sub.2 -Ph.sub.2 P(CH.sub.2).sub.n PPh.sub.2 -Et.sub.3 Al catalyst system (Ph=phenyl, n=1, 2, 3, 4 etc.) for effect of length of the methylene chain between the two phosphorous atoms on cis-1,4-hexadiene formation at 80.degree.-90.degree. C. The data presented for the system CoCl.sub.2 -dppp-Et.sub.3 Al indicate a relatively low yield to 1,4-hexadiene on butadiene.
The temperature teachings in the art have applied whether the conjugated diolefin is butadiene or isoprene. The '194 patent in examples 74-75, 77-82 employs CoCl.sub.2 -dppe-Et.sub.3 Al at 80.degree. or 100.degree. C. to react isoprene with ethylene. In "Preparation of 3-Methyl-1,4-heptadiene, 3-Ethyl-1,4-hexadiene, and Methyl-1,4-hexadienes" by M. Iwamoto, K. Tani, H. Igaki, and S. Yuguchi, Journal of Organic Chemistry 1967, 32, 4148, reaction of isoprene with ethylene is reported rapid and selective (97.2-99%) at 80.degree.-98.degree. C. with the CoCl.sub.2 -dppe-Et.sub.3 Al catalyst system.
Even variants of the cobalt catalyst systems teach reaction conversion of conjugated diolefins to 1,4-dienes at a 80.degree. C. minimum. U.S. Pat. No. 3,445,540 uses a triphosphine instead of a diphosphine, and U.S. Pat. No. 3,574,139 uses cobalt complexed with two diphosphines, i.e., bis [ethylene bis(diphenylphosphine)] cobalt (0) or bis[ethylene bis(diphenylphosphine)] cobalt (I) hydride. Both of these two patents state that "temperatures below 80.degree. C. may be too slow for operating convenience. The preferred temperature range lies between 80.degree. and 120.degree. C. . . ." (3,574,139, col. 3, lines 70-74; 3,445,540, col. 5, lines 35-39).
In the '194 patent, toluene is the solvent in examples 18-23 and 43; halogenated hydrocarbon solvents are used in examples 24-27 and 88. Halogenated hydrocarbon solvents are instructed to be used to improve selectivity when the intended hexadiene is 1,4-hexadiene, and to provide the further advantage of easier cobalt catalyst handling, since these solvents dissolve the cobalt complex completely (col. 4, lines 60-67). In the article by Henrici-Olive et al cited above, halogenated hydrocarbon solvents are said favored, because CoCl.sub.2 -dppe is insoluble in toluene and alkylation reactions of transition metal salts with aluminum alkyls are faster and more complete in halogenated solvents than in aromatics. To the same point is U.S. Pat. No. 3,647,902.
The highest selectivity, essentially 100 percent selectivity, is desired, in order to maximize production of pure 1,4-dienes, thereby eliminating the difficult separation of 2,4-diene and other by-products to satisfy the commercial need for pure 1,4-dienes. An object of this invention is the preparation of 1,4-dienes with essentially 100% selectivity from reaction of conjugated diolefins with an alpha-olefin.
An object of this invention is provision of a process providing essentially pure 1,4-dienes from conjugated diolefins at high rates of reaction.
An object of this invention is provision of a process providing essentially pure 1,4-dienes from conjugated diolefins at high rates of reaction and high catalyst productivity.
In order to obtain highest reaction rates per unit of catalyst, the prior art has employed halogenated hydrocarbon solvents for preformed catalysts, particularly the favored CoCl.sub.2 -dppe/TEAL catalyst system of the above referenced prior art. However, halogenated solvents are environmentally disfavored, are corrosive to equipment, and consequently are commercially unattractive as a means of improving catalytic reaction rates and product yields. An object of this invention is provision of a process promoting reaction of conjugated diolefins and alpha-olefins at high rates of reaction without the use of halogenated hydrocarbon solvents.
We have found that production of essentially pure 1,4-dienes from conjugated diolefins and an alpha-olefin (essentially 100% selectivity) can be realized, using a particular combination of certain cobalt compounds, a particular diphosphine and a dialkylaluminum halide. Surprisingly, contrary to the teachings of the prior art, we have found that this result is achieved at temperatures less than 80.degree. C. Further, we have found this exceptional selectivity at these reaction temperatures in this particular catalyst system is accompanied by vastly increased rates of reaction and catalyst productivity, indicative of a very reactive species of catalyst. Still more surprisingly, we have found these results can be accomplished without use of the corrosive and environmentally disfavored halogenated hydrocarbon solvents that the prior art teaches should be used to improve yields.